Mice homozygous for the Shhtm1Amc targeted mutation display early defects in the establishment and maintenance of midline structures. These defects result from the critical role the Sonic hedgehog (Shh) gene plays in the patterning of vertebrate embryonic tissues, including the brain and spinal cord, the axial skeleton and the limbs. Defects are also observed in all tissues, confirming the proposed role of SHH proteins as an extracellular signal required for the tissue-organizing properties of several vertebrate patterning centers. When bred to a strain with loxP sites inserted into the same targeted allele (Stock No. 004293) and a strain expressing Cre recombinase in the skin and dental epithelium (Stock No. 004782), this mutant mouse strain may be useful in studies of hedgehog signalling and cell proliferation in the dental epithelium. When bred to a strain with loxP sites inserted into the same targeted allele (Stock No. 004293) and a strain expressing Cre recombinase in the mesonephric duct and its developmental derivatives (Stock No. 004692), this mutant mouse strain may be useful in studies of hedgehog signaling and cell proliferation/differentiation in mesenchymal cells of the kidney. The Jackson Laboratory 2024, used with permission.